An example of a radio communication means applicable only in a local area is a non-contact IC card.
Such radio communications are realized based on the principles of electromagnetic induction, for example. In other words, a radio communication system includes an IC card having a memory function, a card reader/writer for accessing a memory of the IC card for reading and writing, and an antenna at a side of the card reader/write and a loop coil at a side of the IC card form single transformer as a system.
On the card reader/writer side, a current to flow in the antenna is modulated so that an induced voltage at the loop coil of the IC card is modulated so as to carry out data transmission from the card reader/writer to the IC card. Further, the IC card sends a reply back to the card reader/writer by the process in which a load fluctuation between terminals of the loop coil changes an impedance between antenna terminals on the IC card reader/writer side so as to change a passing current and a voltage of the antenna, for example.
The non-contact proximity communication system as typified by the IC card is easily operated and therefore widely used. For example, by storing, in the IC card, a secret identification code and other personal authentication information, value information such as an electronic ticket, a cash dispenser and a card reader/writer located at an entrance/exit of a concert hall or an entrance gate of a station may access the IC card presented by a user in a non-contact manner so as to perform an authentication process.
Recently, along with an improvement in fine technologies, an IC card having a memory space of a relatively mass storage has been developed. Such an IC card having a memory space of a relatively mass storage can store a plurality of applications (or services) at the same time so that one IC card may be employed for a plurality of uses. For example, one IC card may have various services such as electronic money for settling an electronic account, an electronic admission ticket to a specific concert hall, etc. stored therein so as to be applied to various uses.
Further, each device may be equipped with both an IC card function and a card reader/writer function so that an IC card technology may be employed as a versatile and bi-directional proximity communication interface.
For example, when the proximity communication system is constructed of devices such as a computer and an information appliance, the communication is carried out one-to-one. Further, a device may communicate with a counterpart device (referred to as a card) other than a device such as the non-contact IC card. In this case, it is possible to employ an application for carrying out one-to-many communication between one device and a plurality of cards.
In such a proximity communication system, the user physically places the devices performing the proximity communication closer to each other so that at least one device may find the other counterpart device so as to automatically start an operation. However, when a distance between the devices increases, the communication may be interrupted at any time. Therefore, there is a need for an operation guarantee mechanism which may prevent the failure of the system even if the user pulls away the devices at any timing.
Some existing proximity communication systems guarantee an operation of writing data of a given size (128 bytes, for example) by means of a function of the IC card itself. However, even in this case, when writing information data larger than the given size of data, data inconsistency may take place depending on its timing.
Specifically, in the proximity communication by means of the IC card where its commination service area is limited to the local area, it is quite probable that the communication could be interrupted. For example, the devices might be pulled away by a user's operation or a barrier could interfere with the devices. Since the IC card increases in its memory size, variations of applications/services and chances of transferring a relatively large data to the IC card increase, a problem of securing the data when the communication is suddenly stopped becomes critical.